(a) Field of the Invention
The present invention relates to a process for preparing polymerized toners, and more specifically to a process for preparing polymerized toners having a higher image concentrations and excellent transcription efficiency and thus being able to exhibit superior performance in the field of developing electronic pictures.
(b) Description of the Related Art
Toners as used for developing electronic pictures, and for electrostatic printers and copying machines refer to a paint capable of being transcribed and fused into an object to form a desired pattern thereon. With computers being more commonly used in word processing in recent years, there have been rapidly growing demands for imaging apparatuses such as printers, resulting in an increase in the use of toners as well.
Typically, toners are prepared by using a pulverization method or a polymerization method. Most widely known is a preparation process by using the pulverization method, wherein resins and pigments are put into a melt-mixing process together, melt-mixed or extruded, and then pulverized and sorted out to give toner particles. However, this process has drawbacks in that the toner particles thus obtained have a broad particle size distribution and very irregular shapes including sharpened edges so that they are inferior in chargeability or flowability.
For the purpose of addressing the above-mentioned problems, a process for preparing spherical toner particles by using a polymerization method was proposed. For such a preparation process of toners by using polymerization, an emulsion polymerization (coagulation process) and a suspension polymerization were known in the art. The process for preparing toners by using the suspension polymerization was preferred since the emulsion polymerization had difficulties in controlling a particle size distribution and reproducing the quality of the obtained toners.
For the preparation of toners by using the suspension polymerization, binder resin monomers and various additives including a pigment, a wax, a charge control agent, or an initiator were uniformly dispersed to provide a monomer mixture, which is then dispersed in an aqueous dispersion in the form of fine droplets before being subjected to a polymerization process. In such a polymerization process, it is very difficult to prepare toner particles with a narrow particle size distribution. In particular, when carbon black is used in order for the polymerized toner prepared by the suspension polymerization to express a black color, the conductivity of carbon black contained in the toner may cause a decrease in the chargeability of the toner, leading to lowered transcription efficiency.
Accordingly, there has been a need for researches to develop a process capable of effectively preparing toners that not only show highly uniform chargeability even with carbon black contained therein so as to enable a realization of high transcription efficiency but also have a narrow particle size distribution, and in particular capable of preparing a polymerized toner enabling a realization of a higher image concentration and excellent transcription efficiency.